1. Field of the Invention
The invention relates to devices for driving light sources, and particularly to a driving device for avoiding a arcing.
2. Description of Related Art
Conventionally, a liquid crystal display (LCD) panel uses discharge lamps, such as cold cathode fluorescent lamps (CCFLs), as light sources of a backlight system. Typically, an inverter circuit, which includes a transformer for stepping up an alternating current (AC) signal, is used to drive the CCFLs. In order to reduce the size of electronic devices, a secondary winding of the transformer is constructed to be very thin, which makes it susceptible to being damaged and can lead to arcing, presenting an unacceptable risk.
Referring to FIG. 4, a block diagram of a conventional driving device for driving a lamp L′ is shown. The conventional driving device includes a power stage circuit 11, a transformer T′, a voltage sensing resistor R1, a compare and latch circuit 12, a controller circuit 13, a protection circuit 14 and two capacitors C11, C12. A primary winding of the transformer T′ is connected to the power stage circuit 11. A high terminal of a secondary winding of the transformer T′ is connected to the lamp L′, and a low terminal of the secondary winding of the transformer T′ receives a DC signal Vin. One end of the voltage sensing resistor R1 is connected to the high terminal of the transformer T′, and the compare and latch circuit 12 is connected between the other end of the voltage sensing resistor R1 and the controller circuit 13.
When there is no arcing on the secondary winding of the transformer T′, both of the AC signal stepped by the transformer T′ and a DC level of the DC signal Vin can be sensed by the voltage sensing resistor R1. However, when there is a arcing on the secondary winding of the transformer T′, only the AC signal stepped by the transformer T′ can be sensed by the voltage sensing resistor R1. Therefore, the conventional driving device only determines whether there is arcing on the secondary winding of the transformer T′ according to the DC level of the DC signal Vin.
Therefore, when the device drives a plurality of lamps, there is need for a plurality of voltage sensing resistors and compare and latch circuits, which increases the cost and complexity of circuit construction of the device, and also requires that the device be larger to accommodate the complex circuitry.